|Zeiss Loxia 50mm - My friend, John [Click image to enlarge.]|
[This is not a discussion for those who shoot Canon or Sigma bodies and also shoot Sony. It's a no-brainer to want to be able to use Sigma's Canon (or Sigma) mount glass on both your bodies.]
The Sigma MC-11 gives Sony E-Mount users access to a range of Sigma lenses. But the first question has to be: What are the practical opportunities?
Sigma has been very clear that its MC-11 Mount Converter is only for still photography; that it only works with a selection of Sigma lenses; and, that it doesn't support autofocus-continuous (more about that later). After hearing that, videographers, sport and action photographers would be thinking (correctly, I believe) that the MC-11 option isn't for them.
It's also important to note that the Sigmas are not weather sealed. A wedding photographer, for example, might find that a deal breaker. On the other hand, the Zeiss Batis lenses are weather resistant and the Zeiss Loxias have mount gaskets to improve their weather resistance. The Sony/Zeiss full-frames are also weather resistant. Samyangs, however, are not sealed.
Today I'm only going to talk about the Sigma "Art" primes. A "zoom" discussion may be for another day.
The Sigma full-frame "Art" primes (20, 24, 35 and 50mm) have shown the world that Sigma is at the top of the full-frame DSLR lens game. As modern, high quality lenses, the Sigmas may be relatively inexpensive, but they are not cheap. And, high-end glass is a long-term investment, so some price disparity can't be a dominant factor.
In the various reviews, the Sigmas are usually, and favourably, compared to Canon or Nikon lenses. And with these comparisons, functionality is not an issue — but in using Sigmas with the MC-11, it is.
With the MC-11, the Sigmas all return distance and full exif data to the Sony bodies. That means that stabilised Sony A7 series bodies will afford the 5-axis stabilisation that they do for Sony and Sony/Zeiss lenses. In my limited experience with the 24mm on the A7RII, the stabilisation works well, and the focusing is both quick and accurate, even in lower light.
For me, however, I don't see an advantage for the Sigma 50 or 35mm lenses over their Sony/Zeiss counterparts. The Sony/Zeiss 55mm, f/1.8 and the 35mm, f/2.8 are outstanding lenses. And, if I really needed a 35mm, f/1.4, it would be the Sony/Zeiss, despite its higher price.
The Sigma 24mm is a stop faster than its Zeiss 25mm cousin, and it's substantially less expensive. (In Australia the Sigma 24mm is less than half the price of the Zeiss 25mm. In the US the Zeiss is about half again the price of the Sigma. But don't forget the cost of the MC-11.)
In 24/25mm, there are still opportunities to use depth-of-field for subject isolation — one of the reason why I like 24mm. So, I don't think that a stop of difference should be ignored.
The Sigma 24 and the Zeiss 25 rate about equally in DXO marks, And, while Sigma says that "autofocus continuous" isn't available on the 24mm using the MC-11 — it is on the A7RII, and with eye focus.
If autofocus is less important to you, you might consider the Samyang 24mm, f/1.4 (manual focus, and manual aperture), but with a native E-Mount (that does not report distance or other Exif data). The Samyang 24mm is fast, very sharp and a bit less expensive. Samyang also offers its 24mm in an E-Mount cine (clickless aperture) version.
I like the 24mm focal length over 35 more generally. And I'll have more to say about the Sigma 24mm with the MC-11, in the future.
The Sigma 20mm has two (sort of) counterparts: The Zeiss Loxia 21mm, f/2.8 (manual focus and manual de-clickable aperture), and the wider, but autofocus, Zeiss Batis 18mm, f/2.8. Both of these Zeiss lenses are two stops slower. And, while both are more expensive, the disparity is substantial, but not huge; and, both are, of course, native E-Mount. (To avoid confusion, there's also a Sony 20mm, f/2.8 A-Mount and a Sony 20mm, f/2.8 for the APS-C "NEX" E-Mount.)
Zeiss lenses are known for their high build quality, their contrast, 3D pop, and colour rendition. I'm dodging those discussions, as those issues are addressed in specific lens reviews elsewhere.
I would like to have seen Sigma shift from native, Sony A-Mount support to native Sony E-Mount. But Sigma has to know that they are in an increasingly crowded field of native E-Mounts, with the Sony, Sony/Zeiss, Zeiss, Voigtlander, Samyang, Lensbaby, Mitakon, and Tamron offerings. The MC-11 also means that both Canon and Sigma body owners, can use a Sony body to make their Sigma lens investments more versatile.
And, hey Sigma, How about a 135mm, f/1.8?